The document discusses various aspects of human vision and the eye. It explains the functions of the iris, pupil, and ciliary muscles in controlling the amount of light that enters the eye and allowing it to focus on objects at different distances. It defines refractive errors like myopia and hypermetropia and how they can be corrected using lenses. It describes Newton's experiment that shows white light is made of the visible color spectrum. It explains why the sky appears blue, sunrises and sunsets have redder colors, and clouds appear white due to the scattering of light. It discusses why stars twinkle but planets do not and why space appears dark.

1. HUMAN EYE AND THE COLOURFUL WORLD
1. Write down the functions of following parts of human eye a)iris b)pupil
c)ciliary muscles
Ans.a)Iris -controls the size of the pupil
b)Pupil – controls the amount of the light that enters the eye
c)Ciliary muscles – hold the lens suspended in position and enables it to
change focal length i.e power of accommodation .
2. Explain the terms. a)power of accommodation b)myopia c)hypermetropia
Ans. a)power of accommodation – the ability of the eye lens to focus near and
far objects clearly on the retina by adjusting its focal length.
b)myopia – the eye defect in which a person can see close objects clearly than
distant objects
c)hypermetropia – the eye defect in which a personcan see distant objects
clearly and cannot see near by objects
3. What is dispersion. Explain an activity to show that white light contains 7
colours.
Ans The splitting of white light into seven colours (VIBGYOR) when passed
through a glass prism is called dispersion of light.
Activity – Newton s experiment
i)a beam of white light is allowed to pass through a glass prism which
undergoes refraction and gets dispersed into its constituent seven colours
ii) these coloured rays are allowed to incident on the second inverted prism
iii) the second prism recombines them into a beam of white light and emerges
from the other side and falls on the screen.
Conclusion – this is due to splitting of white light into seven colours and again
recombining into a beam of white light.

2. 4. Draw the ray diagram showing the correction of myopia and hypermetropia.
Ans
5. Give reasons a) reddish colour sky during sunrise and sunset b) colour of the
sky is blue c) clouds appear as white colour
Ans a) due to scattering of light , red scatters less
b)Fine particles in air scatter the blue colour more than red
c) the tiny cloud particles equally scatters all colours of light , which together make up white light .
6. Explain why a) stars twinkle b)planet do not twinkle c) sky appears dark to
the astronauts
Ans the intensity of star light reaching our eyes increases and decreases
continuously due to atmospheric refraction . When intensity increases star looks
bright and when decreases it looks dim , this gives twinkling effect
b) planets are much closer than stars and all the light coming from single point
enters our eye and so planets looks steady and do not appear to twinkle
c) no atmosphere is present in space. so no scattering of light takes place ,and
hence astronauts see the actual colour of the sky i.e black.

3. 7. An old man cannot see objects closer than 1m from the eye clearly. Name
the defect of vision which he is suffering from. How can this be corrected?
Draw the ray diagram for the defective vision.
Ansa) hypermetropia
b) correctedbyusingappropriate convex lens.
c)
8. A person needs a lens of power -4.5D for correction of his vision. a)what
kind of defect is he suffering from? b)what is the focal length of the
corrective lens? c) what is the nature of the corrective lens
Ans a)myopia
b)f = 1/P = 1/-4.5 = -0.22cm
c) concave lens